Thermotropic liquid-crystalline polyester resin (which is hereinafter abbreviated to “LCP”) has good properties including heat resistance, mechanical properties such as rigidity, chemical resistance and dimensional accuracy. Owing to those properties, LCPs are used not only for manufacturing molded articles but also for a variety of products including fibers and film.
In the information and telecommunication fields, very thin parts are sometimes required. Personal computers and mobile phones in particular employ highly integrated devices and the art wishes to use downsized, thinner and smaller parts for them. Because of the excellent molding processability of the LCPs, i.e., good flowability and less formation of flash, consumption of LCPs has been increasing recently.
For mounting electronic components such as connectors, environmentally conscious lead free solders are preferably used these days. The reflow temperature of the lead-free solders is relatively high and the higher temperature sometimes causes blister formation on the surface of the molded article made of the LCPs.
The blister formation is believed to be caused by air existing in dies and/or hoppers as well as decomposed gas, air and/or water embed in resins.
In addition, the higher reflow temperature may also cause warpage of the molded article made of LCPs. In order to avoid the development of warpage, fillers such as talc have been added to the LCPs.
The development of warpage is suppressed in the LCP compositions comprising talc. However, talc comprises a small amount of water and the LCP compositions comprising talc have the problem of blister formation because of the water introduced simultaneously with talc.
In order to avoid blister formation on the surface of the molded article made of LCPs, various strategies have been proposed. For example, adding additives such as silicone rubber, phosphoric compound or boric compound to the LCP composition (Japanese Patent Application Laid Open Nos. 02-075653, 06-032880, 10-036641, 10-158482, 11-140283, 11-199761, 2003-096279 (corresponding to US2003089887) and 2004-196886, the references are herein incorporated by reference); controlling the screw compression ratio upon injection molding of the LCP (Japanese Patent Application Laid Open No. 11-048278); and adjusting the screw of a kneader for kneading the LCP and the inorganic fillers so that the meshing ratio of the screw is within a certain range (Japanese Patent Application Laid Open No. 2003-211443) have been proposed.
However, methods which comprise adding various additives in order to avoid blister formation are not sufficient in terms of their effects on suppressing blister formation and may involve the problems of significantly impairing the mechanical properties of the LCP compositions depending on the type of additives.
Further, methods which comprise controlling the screw setting upon injection molding or upon kneading LCPs and inorganic fillers have the problem of a heavier work burden compared to the methods which comprise adding additives to the LCPs.
Therefore, the art wishes an improved LCP which exhibits less blister formation on the molded article made of the same without the need for controlling the screw setting upon molding the LCP and without the need for addition of additives to the LCP.